Backflow Tester common mistakes
Backflow Tester · Understand the traps and how to avoid them.
Treating a reduced-pressure principle assembly's relief valve discharge as proof that the differential check valves are holding, and failing to test the check valves separately with the relief valve held closed.
Candidates see the relief valve dump water and assume the whole assembly is failing, or see no discharge and assume it is fine, because they have not internalized that the relief valve responds to the differential across check valve 1 only and tells you nothing directly about check valve 2 or the tightness of either check.
What to do instead
Learn the test sequence as a fixed order: test check valve 2 for tightness first, then check valve 1, then the relief valve opening point, each with the correct gauge placement and isolation. Practice writing the sequence from memory and stating what each gauge reading proves.
Confusing the direction of flow and gauge placement on a double check valve assembly, recording a check valve as passing when the gauge setup cannot actually detect leakage.
The double check assembly has no relief valve, so tightness is inferred from holding pressure with the correct test cock open and the upstream side isolated. Candidates who place hoses on the wrong test cock or fail to bleed air read trapped pressure as a passing check.
What to do instead
Draw the assembly with numbered test cocks and label which cock feeds the high side and which feeds the low side of the differential gauge for each check. Drill the hose routing until it is automatic, and always bleed air before recording a reading.
Applying the wrong unit conversion or reading the gauge to the wrong scale when recording differential pressure, so a borderline assembly is scored as passing or failing incorrectly.
Gauges are read in psi or kPa and some candidates mix units, misread a dual-scale dial, or interpolate the needle sloppily under time pressure, then compare the number to the wrong threshold.
What to do instead
Standardize on one unit for all recordings, convert only at the end, and practice reading a dual-scale dial until the needle position is unambiguous. Write the threshold next to each recorded value before judging pass or fail.
Testing the pressure vacuum breaker or atmospheric vacuum breaker without first establishing the correct supply pressure and flow condition, or testing an atmospheric vacuum breaker while it is under continuous pressure.
These assemblies are sensitive to upstream pressure and to whether a downstream shutoff valve is present. Candidates skip the pressure check or leave a downstream valve closed, and the air inlet does not open at the proper point.
What to do instead
Confirm supply pressure is within the manufacturer's range and confirm the atmospheric vacuum breaker has no downstream shutoff before testing. For a pressure vacuum breaker, verify the air inlet opens at the specified differential and record the supply pressure with the result.
Misidentifying the degree of hazard and selecting the wrong assembly or protection method for the described cross-connection.
Candidates memorize assembly names without linking them to health hazard versus non-health hazard, backpressure versus backsiphonage, and whether the application is high hazard, so they pick a double check where a reduced-pressure principle assembly is required or vice versa.
What to do instead
Build a decision table: hazard level, backpressure or backsiphonage, and whether the assembly must vent. Practice classifying short scenarios aloud and justify the choice with the hazard and flow condition, not the assembly name alone.
Failing to recognize an indirect cross-connection, such as a submerged inlet, a hose bibb with a attached sprayer, or a boiler feed line, and reporting no cross-connection on a survey question.
Candidates look only for direct pipe-to-pipe connections and miss submerged openings, backpressure from boilers or elevated piping, and temporary connections made with hoses, which are the most common real-world cross-connections.
What to do instead
Survey systematically from the meter through every fixture, appliance, and process, asking at each point whether a contaminant could be pulled or pushed back. Practice listing backpressure sources and backsiphonage sources separately for each fixture type.
Skipping the pre-test inspection and setup, such as verifying shutoff valve condition, checking for leaks, confirming gauge calibration, and recording the assembly's make, model, and serial number before testing.
Candidates rush to the gauge because that is what they studied, and forget that a leaking shutoff or a damaged test cock invalidates the test and that documentation must match the assembly on site.
What to do instead
Use a written pre-test checklist every time: identify the assembly, verify valves hold, inspect test cocks and relief valve, confirm gauge condition, and record conditions. Run the checklist on practice assemblies until it is habitual.
Misunderstanding the role of the relief valve opening point and the air gap in a reduced-pressure principle assembly, and judging the assembly only on check valve tightness.
Candidates treat the relief valve as a secondary item because it is last in the sequence, but a relief valve that opens too late or too early is a failure even when both checks hold, and the air gap requirement is often overlooked entirely.
What to do instead
Memorize the relief valve opening point criteria and the requirement that the relief valve discharge be piped to a safe drain with a proper air gap. Practice stating what each failure mode of the relief valve means for the assembly's status.
Recording a test result without stating the test conditions, or reporting pass or fail without the measured values that support it.
Candidates focus on the final verdict and omit the differential readings, supply pressure, and gauge identification, which makes the report unusable and is itself a common scoring loss on documentation questions.
What to do instead
Adopt a fixed report format: assembly identification, supply pressure, each measured differential or opening point, gauge used, and the pass or fail conclusion tied to the measured value. Practice filling the form completely for every practice test.
Assuming that a backflow preventer protects the entire system regardless of where it is installed, and ignoring the need for protection at each point of use or for thermal expansion control.
Candidates learn assembly types but not placement logic, so they place a single device at the service entrance and miss internal cross-connections, or they forget that a closed system with a backflow preventer needs thermal expansion relief.
What to do instead
Study placement principles: containment versus point-of-use protection, and the requirement for expansion control downstream of a device that creates a closed system. Practice mapping a simple building and marking every location that needs protection and why.